1. Field of the Invention
This invention relates generally to refractory linings and more particularly concerns a medium weight abrasion-resistant castable which may be used as a refractory lining.
2. Prior Art
Oil refineries use a significant amount of refractory linings comprising a dual castable lining having a dense abrasion-resistant working face and an insulating back-up. The dual castable is formed from two separate bodies which are held together by the anchoring system when the steel shell is lined. The insulating material is initially applied to the steel shell and then the dense abrasion-resistant material is applied to form the working face of the lining.
The dense abrasion-resistant face extends the life of the lining, but since its thermal conductivity is not sufficiently low, there must be an insulating layer behind the working face. Although such a refractory lining is adequate, since two layers must be installed, the time required to line the steel shell is significantly greater than if a single layer of castable material were used.
As an alternative, the prior art has used a single dense abrasion-resistant lining. However, to obtain adequate abrasion resistance, the refractory linings of the prior art have had to sacrifice the insulating value of the lining due to a higher thermal conductivity of the abrasion-resistant hard aggregate material used. Further, the density of the material makes it more difficult to hold the lining against the steel shell.
According to ASTM, C-401 on Classification of Castable Refractories, an "Insulating Castable" does not exceed a maximum bulk density of 105 lbs/cu ft. Commonly used abrasion-resistant products generally referred to as dense castables have a density which is generally greater than 130 lbs/cu ft after being dried at 220.degree. F. The term "medium weight" is used to describe a castable having a density of between 105 and 130 lbs/cu ft.